The present invention relates to a liquid crystal display and, more particularly, a liquid crystal display having repair lines and methods of repairing a defect thereof.
The liquid crystal display (LCD) is a device comprising a thin film transistor substrate, a color filter substrate, and liquid crystals inserted between the two, whereby the electro-optical effects of the inserted liquid crystals are used for display purposes.
The display method above may use simple matrix method or active matrix method. For LCDs using the active matrix method, thin film transistors (TFT) are generally used as switching devices for controlling operation of each pixel, and the TFT substrate of such LCDs comprises TFTs, pixel electrodes, gate lines for applying signals to pixels aligned in matrix formation, and data lines for applying picture signals.
When a data line of the active matrix LCD is disconnected or defective (hereinafter xe2x80x9cdisconnectionxe2x80x9d will be used to refer to either a disconnection or defect in a data line), the disconnection can be repaired by using lines within the unit pixel or using repair lines placed outside of the substrate of LCD. Under the former method, one must first locate the disconnected data line and then find the point of disconnection on the data line. However, it is difficult to find the point of disconnection and the repair becomes impossible when the disconnection occurs over two or more pixels.
Under the latter method, it is only required to locate the disconnected data line and there is no need to find the point of disconnection. Then only the crossing points of the disconnected data line and the repair line has to be shorted by laser, allowing for a much simpler repairing method.
From this point, the wiring structure of TFT substrate of conventional LCD and its disconnection repairing method shall be explained in detail. FIG. 1 is a wiring structure of conventional TFT substrate having two repair lines in the shape of a closed loop. As shown, a plurality of gate lines (G1xcx9cGn) are arranged in horizontal direction, and a plurality of data lines (D1xcx9cDn) are arranged in vertical direction, and each of gate lines and data lines has an input pad on one end. A pixel is defined by the gate line and the data line. An active area consists of all the pixels.
On the outside of the active area 50 having (nxc3x97m) number of pixels, two repair lines 100, 200 form two closed loop, each overlapping all data lines and gate lines at two points.
FIG. 2 illustrates a repairing method of the TFT substrate shown in FIG. 1. Suppose data line D4 and data line D7 are disconnected at point a and point b, respectively. The data line D4 may be repaired by shorting its two crossing points a1, a2 with the repair line 100 and disconnecting two points marked //, of the repair line 100 with laser so that picture signals could flow through the shorter path. In this way, a picture signal is sent to the disconnected point a of the data line D4 by path P1 from the top, and the signal is sent to the remaining portion of the data line D4 by path P1xe2x80x2.
Then the data line D7 may be repaired by shorting its two crossing points b1, b2 with the repair line 200 and disconnecting two points of the data line D7 marked by //, of the repair line 200 with laser. In this way picture signals as with before are sent to the disconnected point b from top by path P2, and the signal is sent to the remaining portion of the data line D7 below the disconnection by path P2xe2x80x2.
However, the TFT substrate having repair lines outside of the active area in closed loops would experience substantial electrical resistance when repairing a disconnected data line in the middle of active area since the signal path for sending signals to the data line below the disconnection becomes quite lengthy. In addition to large resistance, there would be a substantial parasitic capacitance increase since the repair line overlaps numerous data and gate lines, resulting in increase of RC delay and signal distortion.
Therefore, the conventional repair line structure above is not suitable for a large LCD with many data lines and gate lines. It is also inconvenient since it involves an additional step of disconnecting the repair line to guide the flow of signals through the shorter path around the repair line, as well as a step of shorting the crossing points of the repair line and the disconnected data line. Moreover, the most data lines that could be repaired are limited to four.
An object of the present invention is to solve the problems associated with the conventional repair wire line structure by repeatedly forming a repair line for each of a predetermined number of data lines, thereby minimizing the increase of RC delay resulting from the repair and making data line repair easy.
Accordingly, a liquid crystal display according to the present invention comprises: a plurality of gate lines arranged in horizontal direction; a plurality of data lines arranged perpendicular thereto; a plurality of repair lines formed repeatedly for each of a predetermined number of data lines, the repair lines crossing the gate lines in the active area.
According to a one preferred embodiment of the present invention, the repair line comprises an upper portion crossing top of the data lines, a lower portion crossing bottom of the data lines, and a middle portion which is parallel to the data line connects the upper and the lower portions. A repair line is formed repeatedly for each data-line block including data lines in any multiple of three. A disconnected data line is repaired by shorting the crossing points of the data line and the repair line corresponding to the data-line block of the disconnected data line, making its repair procedure simpler and resulting in shorter signal path after the repair in comparison to the conventional repair method.
Another preferred embodiment of the present invention is directed to eliminating a problem of noticeable pixel brightness difference resulting after the repair with respect to green data line. The middle portion of the repair line is formed adjacent to the green data line and they are connected at one or more points to minimize the generation of RC delay due to the repair so that difference in green pixel brightness would not be noticed.
In another preferred embodiment of the present invention in connection with a liquid crystal display having duplicate gate lines, a repair line includes only a middle portion which is placed parallel to the data lines and secondary gate lines serve as the upper and lower portions of the repair line.